WASHINGTON-Just as more data have implicated spongiform encephalopathies as transmissible, a naked protein, a prion, has become a major suspect as the offender.
A prion is suspected though none has been definitively characterized. Other candidates are a slow virus or virino. The prion-proteinaceous infectious particle-was postulated in 1980 by UCSF’s Dr. Stanley Prusiner.
Several studies have shown that the spongiform encephalopathies are indeed transmissible, even across species. But only a small proportion of inoculated animals develop disease. In a letter to Nature last month, a French team said that a cattle-brain homogenate, taken from animals affected by bovine spongiform encephalopathy, produced spongiform lesions in monkey brains.
In several species, including humans, what’s left over after infected tissues are homogenized and purified is an infectious protein-normal in sequence but deranged in shape.
Studies of scrapie in sheep suggest that different strains of prions are at work, with nucleic acids possibly acting as a template of genetic information. Prions seem to multiply by contact with normal proteins.
Candidate prion strains have been identified through immunohistochemical staining. Two proteins linked to Creutzfeldt-Jakob disease have been isolated from human CSF, says NIH’s Dr. Paul Brown. But identification requires visual selection from more than 400 other proteins. So an NIH team has constructed diagnostic antibodies to these proteins.
British researchers believe that BSE in cattle is caused by a single prion strain-one with unusually persistent phenotypic properties.
WASHINGTON-Just as more data have implicated spongiform encephalopathies as transmissible, a naked protein, a prion, has become a major suspect as the offender.
